OpenJDK JAXB实现中的奇怪NullPointerException Catch [英] Strange NullPointerException Catch in OpenJDK JAXB Implementation

问题描述

我在OpenJDK JAXB中发现了一些奇怪的代码：

I found some strange code in OpenJDK JAXB:

com.sun.xml.internal.bind.v2.model.impl.ModelBuilder

com.sun.xml.internal.bind.v2.model.impl.ModelBuilder

    try {
        XmlSchema s = null;
        s.location();
    } catch (NullPointerException e) {
        // as expected
    } catch (NoSuchMethodError e) {
        ...
    }

有人可以解释他们这样做的原因吗？或者这只是一个需要修复的错误代码。

Can some explain why they do this? Or this is just a bad code need to fix.

推荐答案

他们使用此代码作为测试来确定哪个版本的 JAXB（JSR-222） 正在使用API 。如果 NoSuchMethodError location 参数已添加到JAXB 2.1中的 @XmlSchema 抛出$ c>然后使用JAXB 2.0 API。

They are using this code as a test to determine which version of the JAXB (JSR-222) APIs are being used. The location parameter was added to @XmlSchema in JAXB 2.1, if NoSuchMethodError was thrown then JAXB 2.0 APIs are being used.

参见第158-177行

• http://grepcode.com/file/repo1.maven.org/maven2/org.jvnet.jaxb.reflection/jaxb2 -reflection / 2.1.4 / org / jvnet / jaxb / reflection / model / impl / ModelBuilder.java

• http://grepcode.com/file/repo1.maven.org/maven2/org.jvnet.jaxb.reflection/jaxb2-reflection/2.1.4/org/jvnet/jaxb/reflection/model/impl/ModelBuilder.java

Javadoc - @XmlSchema.location

• http://docs.oracle.com/javase/6/docs/api/javax /xml/bind/annotation/XmlSchema.html#location（）

• http://docs.oracle.com/javase/6/docs/api/javax/xml/bind/annotation/XmlSchema.html#location()

这篇关于OpenJDK JAXB实现中的奇怪NullPointerException Catch的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！